The present invention relates to apparatus for transporting particulate material, such as fragments of ore or coal, in a liquid carrier medium from a lower level to a higher level. More particularly, the invention relates to improvements in apparatus of the type wherein a riser alternately receives a mixture of solid particles and liquid carrier medium from several pipes.
The German publication "Energietechnik" (Vol. 12, December 1970, pages 574 to 576, article by Laszlo Kocsanyi entitled "Hydraulische Forderung mit Rohrkammeraufgeber") describes an apparatus wherein the lower end of a riser alternatively receives a mixture of solid particles and liquid carrier medium from two discrete pipes. The apparatus employs a low-pressure pump which forces the mixture alternately into two parallel looped pipes. The receiving and discharge ends of the pipes contain valves which are actuated to seal the low-pressure pump from the receiving end of one of the pipes and to seal the discharge end of the one pipe from the riser while the pump feeds the mixture into the receiving end of the other pipe (whose discharge end is then free to communicate with the riser), and vice versa. A second (high-pressure) pump is provided to admit clear liquid into the one pipe when the other pipe receives the mixture from the low-pressure pump, and vice versa. Additional valves are provided to seal the outlet of the second pump from the one pipe while the outlet of the second pump is connected with the other pipe, and vice versa. The flow of mixture into the pipes is countercurrent to the flow of mixture from the pipes into the riser.
A serious drawback of the just described apparatus is that the low-pressure pump conveys a mixture of solid particles and liquid carrier medium. Consequently, the parts of this pump are subjected to extensive wear. The same applies for the wear upon the valves which regulate the flow of mixture from the low-pressure pump into the pipes and from the pipes into the riser. Therefore, the maintenance cost of the just described apparatus is extremely high, especially if the apparatus is designed to transport coal or ore from an underground excavation to a level above the ground. Furthermore, each repair work (even minor repairs) necessitates lengthy interruptions of operation with attendant huge losses in output and deactivation of further processing apparatus.
Another serious drawback of the just described apparatus is that the direction of flow of the mixture into the pipes is counter to the direction of flow of the mixture from the pipes into the riser. This often results in clogging of the pipes because expulsion of the mixture from the pipes is preceded by an interval of stagnation during which the particles become separated from the liquid carrier medium by gravity and agglomerate in certain portions of the pipes, particularly in the bights of their loops.
Additional drawbacks of the just described conventional apparatus include extremely high initial cost, particularly in view of the need for utilization of a large number of valves and also because the apparatus must be equipped with a plurality of pressure equalizing devices.